1. Field of the Invention
The present invention is generally related to a magnetic switch and, more specifically, to a vane switch apparatus for use in an automobile engine ignition system wherein the operative components of the switch are shielded from the deleterious effects of electromagnetic interference.
2. Description of the Prior Art
Many types of magnetic switches are known to those skilled in the art. In addition, skilled artisans are familiar with the application of magnetic switches in association with vane switch apparatus used in the ignition system of automobiles.
For example, U.S. Pat. No. 4,311,981which issued to Luzynski on Jan. 19, 1982, discloses an electric switch that is magnetically activated and includes a Hall effect sensor with a permanent magnet fixed on one side of the sensor and magnetic shielding interposed between the sensor and the fixed magnet to direct magnetic flux away from the sensor. When an operating magnet is moved toward and away from the other side of the sensor, it cooperates with the fixed magnet to produce an increased magnetic field through the sensor to activate it.
U.S. Pat. No. 4,677,946, which issued to Tamagne on Jul. 7, 1987, describes an apparatus for positioning two sensor devices. The two Hall effect sensor devices are positioned in a predetermined angular position with respect to each other and with respect to a distributor of an automobile. A first Hall effect sensor is mounted in a primary carrier to form a first alignment means at a firing point of the first Hall effect sensor. A second Hall effect sensor is mounted in a secondary carrier to form a second alignment means in the secondary carrier at a firing point of the second Hall effect sensor. A third alignment device is formed in the primary carrier at the predetermined angle from the first alignment means and the secondary carrier is mounted to the primary carrier so that the second and third alignment means are aligned and the two Hall effect sensors are able to provide output signals displaced by the predetermined angular rotation.
U.S. Pat. No. 4,508,092, which issued to Kiess et al on Apr. 2, 1985, discloses a magnetic sensor for an automobile ignition system. A Hall effect sensor is spaced intermediate a pair of opposing permanent magnets for concurrently generating dual magnetic flux fields within respective airgap regions formed between each of the magnets and the device. Alternatively a magnet is placed between two Hall effect sensors to define the regions. A toothed disk rotatably connected to the crank shaft of the engine causes different teeth to shunt the magnetic fields in each of the regions in a predetermined sequence for generating pulses at the device output indicative of the firing order of the engine.
U.S. Pat. No. 4,369,376, which issued to Ertl et al on Jan. 18, 1983, discloses a magnetic gate which includes a magnet having two poles. One of the poles has generally flat surfaces. A magnetically permeable metal piece bridges the magnetic flux of the magnet from one to the other of the poles. A semiconductor chip is provided with an integrated circuit. The chip is piezoelectrically unsensitive and is applied to the permeable metal piece.
Although many different types of apparatus are known to the skilled artisan for applying magnetically sensitive devices, such as Hall effect sensors, to switches used in automobile distributor systems, certain problems still exist in the application of these devices. When the Hall effect device is subjected to electromagnetic interference, or EMI, there exists a likelihood that false electrical signals will be generated within the circuitry connected to the magnetically sensitive device. In an automobile engine application, these false signals can cause ignition devices, such as spark plugs, to be fired at the wrong time and in the incorrect sequence. The operation of the associated automobile engine will therefore be adversely effected. Certain automobile engine designs avoid this problem by placing the vane switch at an opportune location away from sources of EMI when the arrangement of engine components permits this technique to be used. Other designs utilize cup-shaped rotatable toothed members which are disposed between the magnetically sensitive device and sources of EMI. In this way, the cup-shaped rotatable member shields the magnetically sensitive device and its circuitry from the EMI because the cup-shaped device provides a path to a point of ground potential.
The sensitivity of a magnetically sensitive device to the adverse affects of electromagnetic interference is a function of its location within the engine compartment of an automobile and the relative position of EMI sources with respect to the device. This sensitivity and dependence on shielding by other components creates a disadvantage in the manufacture of automobile ignition systems. It would therefore be significantly advantageous if a magnetically sensitive switch could be provided which is not sensitive or dependent on the physical location of the switch within the engine compartment or the relative location of other devices for us in shielding the switch from the adverse affects of EMI.